Well, for me personally, If I fail a social roll, I've failed it. I don't reload strictly because of that and, in fact, try to not reload at all outside of a full party wipe. I've been reloading more than usual because of bugs and the like but yeah, that's at least one "realistic" point against your tally.
I see the diceroll as a part of every day luck. Did the guard sleep well today? Did his wife happen to leave him? did he stub his toe when he got out of bed, did he win the lottery?
Aside from that it also serves another roleplay purpose: If I'm playing a grumpy old halfling with a meanstreak a mile wide, and a tendency to chew tobacco with his mouth open, my charisma modifier is going to generally be low. Now let's say he wants to intimidate a guard into letting him pass. This is not very likely to happen, but damn wouldn't it be funny if it did? With a straight up stat check this would never happen. A roll at the very least gives the little bugger a chance. It makes for good stories.
